Fracture Behaviour Of Wood Research Articles

EVALUATION OF WOOD DAMAGE AND FRACTURE BEHAVIOR BASED ON ENERGY ENTROPY OF ACOUSTIC EMISSION SIGNALS

In order to assess the damage and fracture behavior of wood under continuous loading, an energy entropy and b-value associated with the acoustic emission (AE) signal were defined to quantitatively describe the release of strain energy during loading. Firstly, the acoustic emission signals of the wood in the three-point bending test were collected. This paper presents the concept of energy entropy according to the definition of information entropy. In order to further evaluate the strain energy intensity released by the damage behavior of the wood specimen, the acoustic emission b-value was defined. Finally, by jointly analysing the dynamics of these two parameters, the test process can be divided into three phases. The results show that even in the elastic phase, micro-destructive behavior occur inside the wood specimen; in the plastic phase, the wood specimen is not only subjected to macroscopic damage, but also often accompanied by fine cracks inside.

Study on damage and fracture characteristics of wood based on acoustic emission b-value and seismic magnitude difference entropy

To assess the damage and fracture behavior of wood under load, a wood damage assessment method was proposed based on acoustic emission (AE) b-values and seismic magnitude difference entropy. First, AE signals from Pinus sylvestris var. mongolica (softwood) and Zelkova schneideriana (hardwood) specimens were collected separately at a sampling frequency of 500 kHz in a three-point bending test. Then, 52 dB was taken as the threshold of the AE event, and the b-value and seismic magnitude difference entropy were calculated at 4-s intervals. Finally, by comparing with the load‒time curve, the b-value and seismic magnitude difference entropy were used to evaluate the damage fracture degree. The results showed that an increase in the b-value indicates the accumulation of strain energy, and vice versa, corresponding to the concentrated release of strain energy. At the same time, the test process can be divided into three stages—elastic, elastic‒plastic and plastic—based on the level of the seismic magnitude difference entropy.

Fracture Behavior of Wood Under Mode I Loading in Tangential Direction

The aim of this study was to determine the fracture behavior of southern yellow pine (Pinus taeda L.) and red oak (Quercus falcata) wood under mode I loading in the tangential-radial and tangential-longitudinal crack propagation systems by a compact tension test method. The results of the study indicated that, in general, red oak had a significantly different fracture behavior than southern yellow pine for each of the two crack propagation systems. The fracture toughness was higher in the tangential-radial crack propagation system than that in the tangential-longitudinal crack system, but there was no significant difference between the two crack propagation systems for southern yellow pine. The specific fracture energy of the tangential-longitudinal crack propagation system for both wood species was significantly lower than that of the tangential-radial crack propagation system. It means that more energy per unit area for the tangential-radial crack propagation system was needed to separate a wood sample into two halves. The difference in the fracture behavior of wood by the crack propagation system can be explained by the structural features of the tested samples since the crack propagation of the tangentialradial system crosses the annual ring and wood fibers can bridge the crack surface.

A two-dimensional lattice model for simulating the failure and fracture behavior of wood

A two-dimensional lattice model consisting of truss elements was developed in this study to characterize the failure behavior under arbitrary loading and fracture behavior of wood. The characteristic of this model is to use the integral analytical procedure to determine the elastic stiffness and ultimate strengths of bonds based on energy and strength criteria, respectively, instead of using the trial-and-error method adopted by the current scholars in the field of timber. To prove the feasibility of the lattice model, the tension test, compression test, shear test, and off-axis test on Korean pine were carried out, and two types of fracture tests of Pinus pinaster were cited. The properties of the truss elements were determined from the basic mechanical parameters of wood. The simulated results from using the proposed lattice model were compared with the experimental data, and good agreements including deformation and stress–strain curves were observed. The lattice model in this paper can accurately simulate the failure and fracture behavior of heterogeneous wood, and this method can promote the use of lattice models in the wood mesoscopic and microscopic fields.

Fracture behaviour of wood and its composites. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract Fracturing of wood and its composites is a process influenced by many parameters, on the one hand coming from the structure and properties of wood itself, and on the other from influences from outside, such as loading mode, velocity of deformation, moisture, temperature, etc. Both types of parameters may be investigated experimentally at different levels of magnification, which allows a better understanding of the mechanisms of fracturing. Fracture mechanical methods serve to quantify the fracture process of wood and wood composites with different deformation and fracturing features. Since wood machining is mainly dominated by the fracture properties of wood, knowledge of the different relevant mechanisms is essential. Parameters that influence the fracture process, such as wood density, orientation, loading mode, strain rate and moisture are discussed in the light of results obtained during recent years. Based on this, refined modelling of the different processes becomes possible.

3D micro-scale deformations of wood in bending: Synchrotron radiation μCT data analyzed with digital volume correlation

A micro-scale three-point-bending experiment with a wood specimen was carried out and monitored by synchrotron radiation micro-computed tomography. The full three-dimensional wood structure of the 1.57x3.42x0.75mm(3) specimen was reconstructed at cellular level in different loading states. Furthermore, the full three-dimensional deformation field of the loaded wood specimen was determined by digital volume correlation, applied to the reconstructed data at successive loading states. Results from two selected regions within the wood specimen are presented as continuous displacement and strain fields in both 2D and 3D. The applied combination of synchrotron radiation micro-computed tomography and digital volume correlation for the deformation analysis of wood under bending stress is a novel application in wood material science. The method offers the potential for the simultaneous observation of structural changes and quantified deformations during in situ micro-mechanical experiments. Moreover, the high spatial resolution allows studying the influence of anatomical features on the fracture behaviour of wood. Possible applications of this method range from bio-mechanical observations in fresh plant tissue to fracture mechanics aspects in structural timber.

The influence of temperature on the mode I fracture behavior of wood

The influence of temperature on the mode I fracture behavior of wood

The effect of microstructure and stress state on the fracture behaviour of wood

Based on a general fracture mechanics approach, this paper attempts to correlate macroscopic fracture properties with micromechanical behaviour in wooD. In the first part, the influence of orientation, cell size and other structural features of wood on toughness, fatigue resistance and fracture morphology is described. Subsequently, experimental observations of crack tunnelling effects are reported which, coupled with direct crack tip strain measurements and a verification of the influence of specimen thickness on fracture properties, confirm the existence of stress state variations across a crack front in wood, and the corresponding effects on fracture behaviour. Irreversible crack-tip deformation modes are identified, involving intercellular debonding, cell twisting and buckling, and the role of stress triaxiality is discussed. A strain criteria for the fracture of pre-notched bulk wood specimens is developed, based on an observed linear relationship between notch root radius and crack opening displacement for fracture initiation.

The fracture behaviour of wood and the relations between toughness and morphology

Wood is a complex composite material that possesses an excellent combination of mechanical properties. In particular the toughness, or work of fracture, is very high, reaching a value in excess of 1.0 x 10 4 J/m 2 , which, mass for mass, is roughly equal to the toughness of steel and higher than that of artificial composites. The high work of fracture of wood is shown to be due to the arrangement of the cellulose microfibrils in the secondary cell wall (S 2 ). The helically wound pattern of these fibrillae is such as to induce a novel form of buckling failure in tension, which produces an elastic behaviour analogous to the yield point of ductile metals. When glass-fibre composites were constructed with a similar morphology, a large increase in work of fracture was observed.